The present invention relates to wireless networks for communication between a number of wireless terminals which are free to join and leave the network at any time. The network may be configured so that all the wireless terminals communicate through a base station, or so that the devices communicate directly with one another.
Wireless networks are intended to offer flexible and cost-effective alternatives to wired networks, for example as Local Area Networks (LANs). An advantage of wireless over fixed networks is the ease with which new networks can be created and with which new devices, known as wireless terminals, can be added to the network. Some wireless network standards exist, for example IEEE 802.11 in the USA and HIPERLAN in Europe, whilst others are under development, for example Wireless Asynchronous Transfer Mode (WATM). Such standards define the format of a transmission frame, within which control and data transfer functions can take place. The format and length of transmission frames may be fixed or dynamically variable.
Known wireless networks, for instance as disclosed in U.S. Pat. No. 5,274,841, typically operate in one of two different configurations:
1 A base station orientated configuration in which wireless terminals can only communicate with each other with the support of a base station, which is responsible for all wireless terminals within a certain radio coverage area. The base station itself may be connected to further wired networks for communications beyond the radio coverage area. The base station may be a separate unit, or it may be a wireless terminal with additional functionality.
2 A peer to peer configuration in which wireless terminals communicate directly with one another. One of the wireless terminals is typically chosen dynamically to perform the control function.
The first configuration is generally considered to be most suitable for networks with a relatively fixed structure, while the second is considered most suitable for the generation of dynamic networks, such as for document exchange at a meeting.
In order for a wireless network to realise the advantage of flexibility, the procedure for wireless terminals joining and leaving the network should be as simple as possible. The act of a wireless terminal joining a network is known as association and needs to be scheduled within the data transmission format defined for the wireless network. Examples of known techniques for association include dynamic framelength slotted ALOHA, described in GB-B-2 069 799, carrier sense multiple access and address based tree resolution algorithms.
An object of the present invention is to improve the flexibility and efficiency of association to a wireless network.
According to a first aspect of the present invention there is provided a method of operating a wireless network, wherein transmission of data takes place in transmission frames of variable length subdivided into a plurality of time slots, the wireless network comprising a controller and a variable number of wireless terminals, the method comprising the controller maintaining a list of wireless terminals currently registered with the network, determining the lengths of successive transmission frames, and allocating time slots within said frame for various purposes, characterised by the controller scheduling a variable number n of association sections in each transmission frame, where n has a minimum value of zero, in response to the current operating characteristics of the network, by which association sections the wireless terminals can register with the controller.
If desired, the association sections may use a contention based protocol.
According to a second aspect of the present invention there is provided a controller for a wireless network having a plurality of wireless terminals, the controller comprising means for maintaining a list of wireless terminals currently registered with the network, means for monitoring the operating characteristics of the network, means for determining the lengths of successive transmission frames and means for allocating time slots within each of said frames, characterised by means responsive to the current operating characteristics of the network for scheduling a variable number n of association sections in each transmission frame, where n has a minimum value of zero.
According to a third aspect of the present invention there is provided a wireless terminal for use in a wireless network constituted by at least one wireless terminal and a controller, the wireless terminal comprising transceiver means for obtaining scheduling information relating to transmission frames in the network, characterised by means for determining whether an association section is available in a transmission frame and in that in response to said means the wireless terminal attempts association during the association section.
The present invention is based upon the recognition, not present in the prior art, that adding an explicit association section to a transmission frame format and enabling this association section to be scheduled more or less frequently depending on system load improves the efficiency and flexibility of operation of a wireless network.
By means of the present invention a wireless network can schedule a variable number of association sections dependent on considerations such as network loading and the number of active wireless terminals.